1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to a method and apparatus for power control for dual uplink transmissions in High Speed Packet Access (HSPA) networks.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min {NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
UMTS is constantly being enhanced to more efficiently support packet switched services because a significant shift from traditional circuit-switched, often constant bit-rate, services to Internet Protocol (IP) packet switched services is expected in the near future. However, UMTS Release 99, based on dedicated resource allocation per user, is not well suited for IP packet data traffic. Therefore, a technology referred to as High Speed Packet Access (HSPA) has been introduced to provide new features for UMTS and offers enhancements in end-to-end service provisioning for IP-based services.
HSPA is comprised of two mobile telephony protocols: High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA). HSDPA allows networks based on UMTS to have increased downlink transfer speeds and capacity. HSUPA is a further technological improvement that provides increased uplink speeds and capacity. Dual-Cell HSUPA (DC-HSUPA) is a further improvement on HSPA by means of carrier aggregation in the uplink. The basic idea of this multicarrier feature is to achieve better resource utilization and spectrum efficiency by means of joint resource allocation and load balancing across the uplink carriers.
In DC-HSUPA, due to increased bandwidth in the uplink, a larger frequency separation is used between transmit and receive frequencies—as compared to single uplink transmission—to assist in the protection of DC-HSDPA reception. For those bands that do not have sufficient separation between transmit and receive frequencies, leakage from signals that are transmitted from the UE affect the reception of signals in the receive chain of the UE and result in a degradation of reception Signal-to-Noise Ratio (SNR). One way to address this issue is to revert to single uplink frequency operation by deactivating the secondary uplink frequency when transmitting using DC-HSUPA hinders receiving using DC-HSDPA in the UE. However, the deactivation of the secondary uplink frequency is beyond the control of the UE as it is a network operation.